The bundle of His is the part of the heart's electrical system that controls the beating of the cardiac muscle. It is made up of myocardial cells that contract when an electrical impulse passes through them, and also contains pacemaker cells that produce those electrical impulses. This bundle is located in the interventricular septum that separates the left and right ventricles from each other.

Directly before the bundle of His in the electrophysiological pathway of the heart is the atrioventricular (AV) node. Together, they make up the area of the heart called the AV junction. The AV node contains only myocardial cells, no pacemaker cells. The bundle of His connects the AV node to the left and right bundle branches that control the contraction of the ventricles. The pacemaker cells within in the bundle can send electrical pulses at an accelerated rate of 40 to 60 beats per minute.

The electrical impulse in the heart originates in the sinoatrial (SA) node, located in the right atrium of the heart. After stimulating the atria, it travels into the AV node and continues through the bundle of His to the right and left bundle branches so that it can reach the ventricles. The contraction of the ventricles then pumps the blood away from the heart through arteries so that it can travel throughout the body.

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The bundle of His was named for Wilhelm His, a cardiologist from Switzerland, who discovered the bundle in 1893. His was also the first to study the idea of bundle branch blocks which can cause the natural pacemaker in the heart to stop functioning correctly due to a blockage in the electrophysiological pathway. These blocks can be caused by cholesterol buildup or congenital heart defects.

Bundle branch block is diagnosed when tests show the blockage on an electrocardiogram (EKG). Most often, bundle branch blocks are treated, if they are found along with other heart problems, by inserting an artificial pacemaker that can control the electrical impulses necessary for the heart to contract at a normal pace. The pacemaker wires are inserted directly into the ventricles where they can stimulate the right and left bundle branches to contract at the same time.

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